Color television



27, 1940- o. VON BRONK 2,191,515

COLOR TELEVISION Filed Jan. 6, 1938.

1 1 .1 Tyx rr iw INVENTOR 07 7 0 VON BRO/VK ATTO R N EY Patented Feb.27, 1940 COLOR TELEVISION Otto von Bronk, Berlin, Germany, assignor toTelefunken Gesellschaft fur Drahtlose Telegraphic in. b. IL, Berlin,Germany, a corporation of Germany Application January 6, 1938, SerialNo. 183,566 In Germany January 7, 1937 3 Claims.

This invention relates to an improvement in the means for and method oftransmitting television images which may be received, at will, either'innatural colors or else in black-white l shading. In this method ablack-and-white contrast film is scanned in the transmitter, said filmcomprising groups of elementary or indi-" vidual images that have beentaken with suitably chosen color filters. At the receiving end, betweenthe light source and the eye of the viewer a filter arrangement is to beinterposed which will transmit only that-part of the spectrum with whichany given partial picture or image had been taken.

The invention is predicated upon the use of the following action: When ablack and white contrast image is projected upon a screen and isilluminated with monochromatic light, say, red, it will be noticed thatthe black portions of the image appear red, while the white portionsthereof will assume this coloration to a less marked degree, with theresult that the latter appear a faint or pale color or neutral. In otherwords, the picture which before was positive is turned into a negativepresenting a red hue.

Now, this fact is utilized in the present invention in the'followingmanner: If film made for the sending equipment consists of constituentpictures made with varicolored filters, is trans- 'mitted over thetelevision system and is projected with white light upon a screen at thereceiver (it being understood that, of course, distinct camera filterscould be dispensed with, while emulsions exhibiting dissimilarsensitiveness to different colors could be used instead for theconstituent pictures), and if this screen is additionally illuminatedfrom a source of light which has the same color as the filter throughwhich the particular frame of the film which happens to be projected hadbeen taken, then the eye of the viewer will have the impression producedby the natural color of the imaged object, provided that the logicalassumptions, to wit, sufficiently rapid sequence of the frame or imagesand suitable composition of the different colors, have been fulfilled.Because of the inversion of luminous values previously mentioned, theprojected film frame must be a negative in order that, upon the screen,the impression of a positive picture in natural colors may be created.

Now, the applicationv of these physical facts to television work turnsout to be extremely simple. Suppose that at the sending end a negativefilm is to be scanned whose composite pictures have been takensequentially, in a cyclic order, by the aid of filters of the threeprimary colors, for instance, red, blue and green. At the receiving endthe image is re-created by light being as white as possible withequipment whose nature is basically immaterial, say, by the aid of amirror drum and a gaseous-discharge or glow-tube presenting whitishluminescence or a Kerr cell with a glow-lamp or arc-lamp. The image maybe projected either upon a screen or else may be viewed by transluxaction upon a frosted or ground-glass pane. Itwould also be possible touse a Braum (cathode-ray) tube, with the image being viewed upon theluminescent screen itslf or upon a projection surface.

Now, in the neighborhood of the viewing surface are mounted vari-coloredlamps disposed so as to irradiate the picture surface, though theyshould be concealed from the direct view of the observer. These lampsshould fulfill the demand that they will be ignited and extinguished at'the rate and rhythm of the color .change, in the absence of anyappreciable inertia. If the image frequency or frame frequency is 60 persecond, with three colors, each lamp would be switched on and off 20times each second, and it would burn about ,60 of a second. It wouldthus seem that gaseous-conduction (or glow) tubes are particularlyadapted to the present purpose. Recourse could be had either to theinherent or natural color of the glow column of different gases (say,neon gas to produce red and mercury-vapor for blue), or else the desiredhue or color could be secured by the insertion of a suitable filter orelse coloring of the lamp bulb JI tube. Moreover, glow-lamps possessinga low inherent thermal inertia would be suited, and finally alsoluminescent tubes in which, similarly as-in a Braun tube, a luminescentsubstance is caused to luminesce by electron irradiation or bombardment.In this instance, by suitable admixtures incorporated in the luminescentsubstance, or suitable choice of the luminescent substance or phosphorthe desired color effects could be produced. (For instance, extremelypure zinc sulfide furnishes blue light.) v

The cutting in circuit of the different lamps is insured in synchronismwith the change of the picture at the sending end. To effect such achange in connections, recourse could be had again to various ways andmeans. In the simplest case, a revolving switch comprising mechanicalcontacts could be employed, the switch being driven from a synchronousmotor. The drive frequency is transmitted from the television llvtransmitter, or else it is generated at the receiving end byar'generator of stable frequency. If a mirror drum is employed at thereceiving end, or a mirror screw or a perforated disk is used to act asthe picture re-creator, then the revolving switch could be in directcoupling relationship with the mirror drum. However, even if for thedrive of the switch a distinct motor is provided, the latter may be ofsuch reduced dimensions that the synchronizing power may be made readilyavailable. This is an essential advantage over the use of a rotatingfilter organization since such'an arrangement would require considerablymore driving power because of its larger dimensions.

However, quite a number of ways and means are conceivable in which sucha change in connections is accomplished also without the use ofrevolving mechanical parts. Among these may be mentioned the cathode-rayswitch in which a pencil of cathode-rays is caused to sweep over a bankof target electrodes, with the result that the circuits associatedtherewith are sequentially may be regarded as well known from theearlier art. Their operation is predicated upon the periodic chargingand discharging of an electric energy accumulator or storing means suchas a condenser. It would be feasible to directly feed the colored lampsor tubes with the current or potential impulses supplied from thetime-base or ratchet arrangement. It is suitableto provide an auxiliaryor igniter electrode of a kind well known in the art inside theglow-tube. The time-base potentials are impressed upon these auxiliaryelectrodes, and they may be comparatively low,

while the burning potential is furnished from apowerful source of supplysuch as the illumination circuit or power mains. If glow-tubes are usedfor illumination, these could be included in the actual ratchet ortime-base circuit organization, for the purpose of insuring thedischarge of a storing condenser, as soon as the latter has been chargedup to the firing potential of the associated glow-tube.

As previously pointed out, the black-white contrast image re-created atthe receiving end must be a negative if it is to appear as a coloredpositive picture under vari-colored illumination. However, it is by nomeans necessary for this purpose that the image itself should beactually a negative when sent out from the transmitter. On the contrary,it is possible to provide and use reversing means at the receiving endpredicated for their operation and function upon electrical methods.(Details of the methods which would be adapted to the said end need notbe dwelt upon at this time since means for picture reversal in anamplifier stageor in a Kerr cell have been disclosed exhaustively inHandbuch der Bildtelegraphie und das Fernsehen, by Fritz Schroeter,pp.315-317 to which reference is here, made.) At any rate, this offers thenotable advantage that images transmitted in the usual manner may againbe picked up and re-created by any standard black-white contrast imagereproduction and picture receiving means. It will be understood that itis readily possible to utilize at will a blackwhite picture receiver assuch or for colored image reception by the use of the color-filterattachment hereinbefore disclosed. It may be suitable to provide onlyone operating handle or knob which will insure or render operative andinoperative at the same time the reversal of the image in the amplifier(cutting in or out a reversing stage) and the color-light device.

The means adapted to furnish the additional 11- Q lumination turns outto be especially simple when working with the two-color method. The twoprimary colors of the camera or picture-taking filters are in such casegreen and red, in other words, a pair of complementary colors. Now, itcan be shown that it is sumcient to illuminate the screen red whentransmitting the partial image taken with the red filter, while for thepartial picture that had been taken with the green filter no additionalor supplementary illumination is required. It has been ascertained thatthe eye-and this is a physiologically explainable factupon extinction ofthe red, supplementary illumination spontaneously furnishes thecomplementary green, that is, that it perceives or senses a greenstimulus. Now, this phenomenon could be further boosted by imparting aslightly greenish tinge to the permanent or background light with whichimage re-creation takes place. If 8. Braun tube is used for picturereception, then the fluorescent light which mostly is inherentlygreenish in the usual fluorescent or luminescent screen, will assist andboost the said physiological effect. Of course, the procedure could alsobe reversed by choosing green as the sole and only supplementaryillumination rather than red.

In order to secure uniformly satisfactory image re-creation, it will beadvisable to pay particular attention to the geometrical disposition ofthe sources supplying supplementary illumination, and

to the proper balancing of the brightness or intensity of the variouscolored lamps or tubes. It will be found recommendable to provide foreach one of the various colored lamps or tubes, or for all but onecolored lamp (that is, excepting the one used to act as the fixed ordeterminant quantity) a distinct regulating resistance or rheostat; orelse to tap the potential to be impressed upon each one of the variouslamps or tubes from an adjustable voltage divider. It is thus possibleto balance and trim the brightness or luminous intensity of each of thedifferent lamps or tubes so that when blended and mixed there willresultpure white. It would thus, also be possible to shade or blend a givenimage so as to suit personal tastes.

A number of exemplified embodimentsto illustrate the geometricalmounting of the colored lamps or tubes are shown in the appendeddrawing, wherein Figures 1, 2, 3 and 4 illustrate different embodimentsof the present invention.

Referring to the drawing, the screen upon which the image is projectedfor direct viewing or by transmission (trans-lux) and which may be theluminescent screen of a cathode-ray or Braun tube or projection surfaceis indicated at S. The lamps or tubes producing red, blue and greencolors are denoted by r, b, and g, respectively. A reflector or maskingsurface is indicated at R.

Figure 1 shows a' rectangular picture screen around which are groupedpairs of red, green and blue lamps or light sources. These lamps are oftubular shape. They are either glow-tubes or gaseousor vapor-conductiontubes and colored bulbs or attached filters or glow-lamps (incandescentlamps) furnished with elongated filaments involving low thermal inertia.Inasmuch as different filling gases of a glow-tube produce differentluminous intensities, the length of the various lamps will have to beappropriately chosen because of this fact. That is to say, a lamp filledwith a gas luminescing at greater brightness will haveto be chosen ofcorrespondingly reduced length. At any rate, it is convenient to sodispose the lamps that they will produce as thorough and as uniform aspossible an illumination of the picture area or image field. In fact, itis for this reason that more than one lamp or tube should be chosen foreach color.

By choosing a suitable shape for the lamps, it is possible asillustrated in Fig. 2 to make conditions so that the lamps will snuglyand uniformly fit and surround the contour of the picture area. It goeswithout saying that it is advisable to screen the lamps from theobservers view and eyes in order to prevent dazzle, and the meansprovided for the screening could serve at the same time as a reflectordesigned so as to direct the light-rays towards the picture field. Undercertain circumstances, it will be found expedient to diifuse and scatterthe colored light in order that it may become uniformly distributed overthe picture field. For this purpose, there is interposed a ground orfrosted glass or opal pane or else the bulb of the lamps could be mattedor delustered.

Figure 3 shows another mode of mounting the lamps. Four of each colorare here provided, and they are staggered towards the viewer. The resultis that the image field is thoroughly and uniformly illuminated by eachof the colors. A reflector R, as previously indicated, serves forscreening the lamps from the viewers eyes and for condensing or focusingthe light-rays.- 7

One way of distributing the lamps in the case of .a two-color system isillustrated in Figure 4. Only red and green lamps are provided. If thephysiological action previously referred to, that is, for spontaneousaddition of the complementary color, is to be used, then all of the fourlamps may be red or else the lamps designated by 9 could be dispensedwith. Of course, also th'ered color could be spontaneously complementedand only green be used for actual illumination.

One way of simplifying the scheme and present organization would be tocause a single glowtube or gaseous-conduction lamp to alternately glowin two colors. For instance, the tube or lamp could be filled with twodifferent gases or with one gas and one metal vapor which presentdissimilar striking (starting) and ionizing potentials. Thus, bychanging the connections of the tube so that only one of twoglow-discharges will be initiated, thereby resulting in the particularcolor or hue characteristic therefor. Inasmuch as glow-tubes of thiskind are known from the earlier art of advertising sign illumination,there is no need to enter into details in the present disclosure.

It should be mentioned in conclusion that one particular advantage ofthe new receiver system may be seen to reside in the fact that theincoming image is not only not weakened by the filters, butthat it iseven intensified somewhat by the provision of the additional lightsources.

I claim: 7

1. The method of producing substantially natural color television imageswhich comprises the steps of cyclically transmitting signals eachindividually representing a different color value of the subject,producing a series of negative black and white images on the viewingscreen, and simultaneously and successively illuminating the screen bydifferently colored light sources in synchronism with and correspondingto the images produced by the transmitted signals.

2. A television system for producing substantially natural color imagescomprising means for successively and cyclically producing negativeblack and white images on a viewing screen, each individual image of thecycle being representative of a different color value of thesubjectbeing transmitted, a plurality of sources of differently coloredlight, and means whereby the screen may be simultaneously illuminated bysaid sources individually and in succession and synchronism with theindividual images representing the different color values.

3. A television system for producing substantially natural color imagescomprising means for successively and cyclically producing negativeblack and white images on a viewing screen, each individual image of thecycle being representative of a difierent'fundamental color value of thesubject being transmitted, a plurality of differently colored lightsources, and means whereby the screen may be simultaneously flooded bylight from said sources individually and in succession and synchronismwith the individual images produced on the viewing screen.

arm you BRONX.

